One of the most interesting features of A Treatise Concerning the Principles of Human Knowledge is the symbiosis between a radical empiricism and a bold and uncompromising idealism. An artful combination of analytical rigor and unfettered speculation, of crystal-like precision of language and winged metaphors or sparkling images, George Berkeleys work is essentially a God-centered philosophy that argues that something exists only insofar as it is perceived by the mind.